Fine But Not Amazing
There are several RV Parks in the Oceanside area, or that are nearby beaches. We've had a great time across the street at Paradise Pier. The Oceanside RV Park, however, leaves quite a bit to be desired. There are quite a few areas that seem to be under constant renovation, as well as many long-time visitors, which isn't really our scene. And while it is close to the beach, it also borders an active train track. There are other better options.
That said, there are two reasosn why you'd want to stay at Oceanside if other places were not available. First, their, dog run is quite a bit larger that other places and second, they have a strange fake grass tent area where you can stay without at RV, which is one of the only "resort" type places where I've seen that in the area.